From Issue 33 and I think it was republished in a later issue as well:
NV4500 LUBRICANT TESTS FOR HORSEPOWER DRAG
In Issues 30 and 31 we discussed lubricants for the New Venture 4500 5 speed transmission. Dodge recommends Castrol Syntorq. We found that Standard Transmission & Gear in Fort Worth, TX (800-STD-TRAN) offers a good price (about $60 with shipping) on a gallon of Syntorq (the required amount). Several Rammers have urged us to test other lubricants, especially synthetics with higher rated (e.g. GL-5) additive packages. For simplification of this issue, we have developed three initial considerations for testing: (1) lubricant horsepower drag; (2) lubricant temperature under different driving conditions; (3) shifting quality and life of the synchronizers, etc. in the transmission.
We recently dyno tested 5 lubricants for coastdown horsepower drag in the NV4500. [Thanks to Diesel Dynamics for dyno time, expert operation of the dyno, and donating one of the lubes we tested.] The Syntorq was Mopar PN 4874459. Several coastdown dyno runs were made with each lubricant, from 110 mph down to 90 mph. Power runs were made to warm each lubricant to 130 degrees F and 140 degrees F. Lubricants were drained using a 3/8 NPTdrain plug that had been installed in the side boss at the bottom right rear of the transmission main case. Residual lubricant was sucked from the transmission with a turkey baster that had a piece of clear plastic tubing on its tip. In that way, cross-contamination of lubricants was minimized.
Three name brand 75-90 synthetic gear lubes, GL5 or GL6, were tested and had noticeably more drag than Castrol Syntorq. One other lube, Torco Racing Transmission Fluid (RTF), had almost the same drag as Castrol. At most points on the curves that were checked, RTF had about 0.1 hp more drag than Castrol Syntorq. The RTF is rated 75, 80 and 85 weight, and GL-6. Torco said it does not have the "aggressive" additives that are hard on soft metals. They have tested it extensively in road racing with transmissions such as the Corvette 6 speed. They believe there won't be any problems with the brass, synchronizer liners, or bonding resin. The differences in drag among the lubricants were small but reproducible and represent one factor that may have significance in selecting a lubricant for your NV4500.
We have been testing this RTF in a Ram’s NV4500 for some weeks and it seems to perform fine with respect to shifting, noise, and temperature. However, if you choose any lube other than Castrol Syntorq 75-85 weight synthetic gear lube, we feel you need to monitor transmission vs. differential temperature for a while and under different conditions to ensure the lube keeps the transmission as cool as Castrol does. In fact, it is worthwhile to monitor the temperatures with Castrol as well so you can establish a meaningful baseline and because you can spot some problems (such as a fifth gear that is “cocking” on the mainshaft) by increased lubricant temperatures. Through the summer, we will evaluate the temperature and shifting properties of Torco RTF in this transmission, compared to the excellent baseline history of Syntorq.
In summary, then, we recommend that anyone who wants to try lubes other than Castrol use a temperature gauge with two senders, one in the transmission fill plug and one in the differential (get brass 3/4 NPT plugs and drill and tap for the 1/8 NPT sensor. Then you can monitor absolute temps and relative temps between the two. The latter is valuable to see if one lube makes the transmission run hotter than another lube. In other words, you would see if the transmission is at the same temp as the differential under different conditions, or the transmission is getting much hotter (not good). Castrol usually keeps the transmission temperature down. Depending again on what differential fluid you use, it may or may not be cool but still serves as a comparator because the temperatures of both vary with ambient temperature and load.
Results from the dyno tests, in friction (drag) horsepower, at 130 degrees F, are summarized below. At each temperature, six different miles-per-hour (mph) were selected arbitrarily and the results were printed out automatically on the graphs by the data system for those cursor positions.
MPH Syntorq Torco RTF 75/90 GL-6 75/90 GL-5+ 75/90 GL2-5
107.98 26.1 26.2 26.8 26.4 26.9
101.69 21.3 21.5 21.9 21.7 22.0
101.36 21.2 21.3 21.5 21.4 21.8
99.32 19.9 20.0 20.5 20.2 20.5
96.01 18.0 18.0 18.6 18.3 18.4
90.91 15.7 15.7 16.2 16.0 16.1
Results from the dyno tests, in friction (drag) horsepower, at 140 degrees F, are summarized below:
MPH Syntorq Torco RTF 75/90 GL-6 75/90 GL-5+ 75/90 GL2-5
107.22 25.1 25.2 25.6 25.5 25.4
102.29 21.5 21.7 21.7 21.8 21.8
98.94 19.5 19.5 19.8 19.9 19.8
94.73 17.2 17.3 17.5 17.5 17.5
93.70 16.7 16.7 17.0 17.1 17.0
91.91 16.0 15.9 16.1 16.0 16.3
What can we gather from the above data tables? None of the other lubricants were better than Castrol Syntorq for low horsepower drag. One other lubricant, Torco RTF, was specially formulated for transmission use. This lubricant was very close to Castrol in horsepower drag. If you are concerned about using a lubricant that is “only” GL-4 rated (and this rating is usually considered adequate for transmission gears), Torco RTF may turn out to perform very well, while giving a GL-6 protection package. Some folks who have added a lot of horsepower and torque feel that a GL-5 or GL-6 additive package is a good idea. Finally, if you prefer some other gear lubricant for whatever reason, try it but monitor transmission lubricant temperature as a minimum to verify its performance.
Attention: TDR Forum Junkies 
